Endothelial progenitor cell (EPC) dysfunction may contribute to vascular dysfunction in type 2 diabetes (T2DM) and aging because EPCs are progenitor cells that participate in vascular growth and repair. EPCs may be dysregulated in older age and T2DM by reduced mobilization from bone marrow and impaired function once in the circulation. My preliminary data suggest that aerobic exercise training may increase EPC and vascular function in T2DM, but that the effects may be reduced in older age. This study tests the hypothesis that reduced EPC mobilization and function adversely affect vascular function in T2DM, and that and that there are age-associated differences in the effects of AEX training on EPC mobilization and function in T2DM, which will affect AEX-induced changes in angiogenesis and endothelial vasoreactivity. This will be accomplished by specific aims that 1) Determine the effects of 6-month aerobic exercise training on EPC number and EPC mobilization factor expression in older subjects with T2DM compared middle-aged T2DM subjects and normal controls; and 2) Determine the effects of 6-month aerobic exercise training on mechanisms regulating EPC function and migration in older subjects with T2DM compared middle-aged T2DM subjects and normal controls. I will study sedentary, overweight/obese (BMI >25 kg/m2), middle-aged (50-65 yrs) and older (65-80 yrs) adults with T2DM and an age- and BMI- matched group of healthy controls. All subjects will be studied before and after 6-months of aerobic exercise training. An acute bout of exercise will be used to assess EPC mobilization at each time point to determine whether EPC mobilization is reduced in older vs. middle-aged T2DM subjects and normal controls, and also whether aerobic exercise training improves EPC mobilization. In the same subjects, ex vivo EPC tube formation, migration, and gene expression will be measured to determine whether specific markers of EPC function are reduced in middle-aged and older T2DM compared to controls and are improved with exercise training. Endothelial vasoreactivity and skeletal muscle capillarization will be measured to determine whether increases in EPC mobilization and function are associated with improved vascular function in T2DM and whether this differs between older and middle-aged T2DM subjects. This mentored, patient-oriented translational research study will provide me with the training to determine mechanisms of EPC dysfunction at the molecular and cellular level, and translate those findings to tissue (skeletal muscle capillarization) and the whole body level (endothelial vasoreactivity). Results of this study will enhance our understanding of EPC and vascular dysfunction and may lead to therapeutic and pharmacologic strategies to reduce vascular dysfunction in T2DM. This Paul B. Beeson Patient-Oriented Career Development Award will allow me to transition to an independent research career and become a leader in translational research in vascular biology in aging and diabetes.